1. Field of the Invention
This invention relates to cyclone separators, and more particularly, to cyclone separators for use in high temperature operations with highly corrosive, halide-containing gases.
2. Description of the Prior Art
Cyclone separators comprise well known means for separating gases and solids from mixtures of the same. Such separators generally are constructed of the tubular or cylindrical-shaped main body connected to a lower tapered conical portion. A tangential side inlet is provided near the top of the cylindrical main body. A gas outlet tube is provided and generally extends downwardly through the cyclone top into the main body of the cyclone. The tube usually must extend down to a level slightly below the lowest portion of the inlet to assure efficient separation of solids and gases.
In operation solids-laden gases are introduced at high velocity through the tangential inlet. They follow a vortex shaped path around the outside of the gas outlet pipe downwardly towards the bottom of the separator. The solids are deposited along the walls be centrifgal force and separated from the gas. The separated gas then follows a vortex path upwardly and passes out of the top of the cyclone separator through the gas outlet tube. The separated solids flow through a solids outlet at the base of the tapered conical section.
In prior apparatus, for high temperature service, the cyclone interior and gas outlet pipe have been refractory-lined or coated with materials such as alumina, silica, magnesia, beryllia or silicon carbide. Such apparatus have failed to provide satisfactory results in continuous operations since stresses due to thermal gradients and differential thermal expansion cause the refractory to disintegrate or crumble.
In more recent apparatus, such as in U.S. Pat. Nos. 3,327,456 and 3,470,678, cyclones have been constructed using refractory coated hollow gas outlet tubes through which a cooling fluid such as steam or hydrocarbon gases is passed to decrease thermal stressing effects.
While U.S. Pat. No. 3,327,456 is an improvement over the prior art, certain difficulties have been encountered with the design. For example, when a cooler incoming steam or other coolant enters one of the multiple compartments, at the top, it tends to cool the metal in that region to quite low temperatures. As the coolant passes downwardly through the compartment, around the end of the baffle and back upwardly through an adjacent compartment, it is heated to higher and higher temperatures. As a result, the top of the adjacent compartment, where the fluid exits, is at a much higher temperature than the equivalent region at the top of the compartment into which the coolant was introduced. As a result, the outlet tube is subjected to quite severe stresses and strains due to the many sharp and sudden variations in temperature at adjacent points around the circumference of the tube. This also distorts the tub and can cause cracking of the refractory. It also puts a severe strain on the supporting members, which in the case of U.S. Pat. No. 3,327,456 are located inside the cyclone. Such a location is required in order to support the gas outlet tube (which consists of two metal tubes, the lower tube being hollow and both being coated with a refractory material). Further, maintenance upon such a design is considerably more difficult since the support mountings are inside the cyclone for the gas outlet tube.
U.S. Pat. No. 3,470,678 provides a further improvement over U.S. Pat. No. 3,327,456. In U.S. Pat. No. 3,470,678 a triannular, fluid-cooled refractory coated outlet tube is employed. The tube consists of three concentric passages or annular spaces formed from four concentric metal tubes to allow for the flow of coolant. The innermost and outmost metal tubes are coated with refractory to protect the metal from the high temperature gases and solids inside the cyclone. That design also has the disadvantage of increased weight due to the refractory coatings and multiple tube construction.
Special problems arise in the separation of gas-solids suspensions when the gas is a highly corrosive, halide-containing gas mixture and is at an elevated temperature, e.g., in the range of from about 1500.degree. F. to 2400.degree. F. such as the product off-gases from a titanium tetrachloride chlorinator.
In separating such gas-solids suspensions with gas outlet tubes coated with refractory material, both thermal stressing and corrosion result in failure of the gas outlet tube with a consequent decrease in the efficiency of the separator as a greater amount of a fine solid particles are allowed to escape with the separated gas.
Cooling of the refractory coated gas outlet tube to a degree wherein corrosion will be reduced can result in the deposition of solid non-volatile metal halides by sublimation upon both the interior and exterior surfaces of the gas outlet tube. The result of such uncontrolled deposition can be complete blockage of the gas outlet tube in some cases. Accumulations on the exterior of said gas outlet tube can also block gas-solids flow into the cyclone. Further, if a sufficient quantity accumulates such that gravity causes it to break away from the gas outlet tube and fall into the cyclone, blockage of the solids outlet can occur.
The corrosive action alone can eventually result in refractory disintegration. If the gas outlet tube is fluid colled, possibly cooling fluid itself could contaminate the mixture undergoing separation. The entry of cooling fluid into the interior of the separator presents two problems. In one instance, the cooling fluid could enter the solids outlet and be returned to the high temperature gas-solids source, such as a chlorinator, wherein an explosion could occur destroying the equipment and contaminating the atmosphere with highly corrosive, potentially poisonous gases. In the second instance, corrosive, halide-containing gases may contaminate the cooling fluid and cause destructive corrosion of the cooling system pumps, heat exchangers and storage facilities resulting in potential atmospheric contamination as well as economic losses.
Thus, it would be desirable to provide an apparatus wherein the difficulties previously described hereinbefore could be overcome, and further provide a design which provides ease of maintence and installation.